Wednesday, January 27, 2016

Market design doesn't stop when the market opens, and it isn't all analytical--a lot of it is operational, with changes being called for as experience is accumulated. One of the big problems faced by all of the multi-hospital kidney exchange networks is that many proposed transplants don't go through. For example, if a three way cycle is proposed and one of the proposed transplants isn't accepted, none of the three proposed transplants go through. Counted this way, initially only 15% of proposed transplants were realized, but changes in the way surgeons' preferences are elicited has now brought this nearer to 50%. (It turns out it's not easy to elicit surgeons' preferences in advance, but we're making progress:)

Here's an account of some of the ongoing market design in kidney exchange, at the Alliance for Paired Donation. The American Journal of Transportation has now made it open access, after naming it among the 10 "best of AJT 2015" articles.

Abstract: Failure to convert computer-identiﬁed possible kidney paired donation (KPD) exchanges into transplants has prohibited KPD from reaching its full potential. This study analyzes the progress of exchanges in moving from ‘‘offers’’ to completed transplants. Offers were divided into individual segments called 1-way transplants in order to calculate success rates. From 2007 to 2014, the Alliance for Paired Donation performed 243 transplants, 31 in collaboration with other KPD registries and 194 independently. Sixty-one of 194 independent transplants (31.4%) occurred via cycles, while the remaining 133 (68.6%) resulted from nonsimultaneous extended altruistic donor (NEAD) chains. Thirteen of 35 (37.1%) NEAD chains with at least three NEAD segments accounted for 68% of chain transplants (8.6 tx/chain). The ‘‘offer’’ and 1-way success rates were 21.9 and 15.5%, respectively. Three reasons for failure were found that could be prospectively prevented by changes in protocol or software: positive laboratory crossmatch (28%), transplant center declined donor (17%) and pair transplanted outside APD (14%). Performing a root cause analysis on failures in moving from offer to transplant has allowed the APD to improve protocols and software. These changes have improved the success rate and the number of transplants performed per year.
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It turns out that several of my papers in the past year were about kidneys, with a focus on operational issues:

Anderson, Ross, Itai Ashlagi, David Gamarnik and Alvin E.
Roth, “Finding long chains in kidney exchange using the traveling salesmen
problem,” Proceedings of the National
Academy of Sciences of the United States of America (PNAS), January 20,
2015 | vol. 112 | no. 3 | 663–668, http://www.pnas.org/content/112/3/663.full.pdf+html